Minor changes

* Removes commented code
* Renames solo mode into "Playlists"
* Adds/rewrites some comments
Merge branch 'dev/solo'

Conflicts:
	src/ch/epfl/unison/ui/AbstractMenu.java
	src/ch/epfl/unison/ui/GroupsActivity.java
	src/ch/epfl/unison/ui/GroupsMainActivity.java
	src/ch/epfl/unison/ui/GroupsPlayerFragment.java
	src/ch/epfl/unison/ui/NfcManagementActivity.java
	src/ch/epfl/unison/ui/SoloPlaylistsActivity.java